Method for making heterocyclic block copolymer

ABSTRACT

Thermally stable aromatic heterocyclic block copolymers are prepared by reacting a diamino monomer and terephthalic acid to form a carboxy-terminated rigid rod segment and then polymerizing a carboxy-monoamine monomer therewith to form flexible segments grafted onto the rigid rod segments.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

This is a division of application Ser. No. 610,912, filed May 16, 1984,now U.S. Pat. No. 4,544,713.

BACKGROUND OF THE INVENTION

This invention relates a method for preparing aromatic heterocyclicblock copolymers.

In general, aromatic heterocyclic extended chain polymers are well knownfor their outstanding thermal, physical, and chemical properties. Arnoldet al, U.S. Pat. No. 4,108,835, disclose extended rod-likebenzo-bis-oxazole and benzo-bis-thiazole polymers having superiormechanical properties as well as a high degree of thermal and hydrolyticstability. However, these materials presented special processingproblems because of the extended-chain, rigid-rod, structural characterof their molecules.

In accordance with the invention defined in U.S. Pat. No. 4,207,407, toHelminiak et al, it was found that the processing problem could beovercome by blending a coil-like, aromatic, heterocyclic polymer with arod-like, aromatic, heterocyclic polymer. An improved method forblending coil-like and rod-like polymers is disclosed in U.S. Pat. No.4,377,546, to Helminiak et al.

Wolfe et al, in application Ser. Nos. PCT/US82/01285 and PCT/US82/01286,both filed Sept. 17, 1982, disclose aromatic heterocyclic blockcopolymers made up of rigid and flexible segments. These copolymers areprepared by separating polymerizing the rigid segments and the flexiblesegments onto the rigid segments.

We have found that these block copolymers can be prepared by a simplerprocedure.

Accordingly, it is an object of the present invention to provide amethod for preparing aromatic heterocyclic block copolymers having rigidand flexible segments.

Other objects and advantages of the present invention will be apparentto those skilled in the art.

DESCRIPTION OF THE INVENTION

In accordance with the present invention, there is provided a method forpreparing aromatic heterocyclic block copolymers having rigid andflexible segments of the general formulas: ##STR1## wherein Y and Z arethe same or different and are selected from the group consisting of ═NH,═S, ═O and ═NC₆ H₅ ; m is an integer equal to the number of repeatingunits and has a value such that the rigid segment has an intrinsicviscosity of about 8 to 31 dl/g as determined in methanesulfonic acid atRT; and n is an integer equal to the number of repeating units and has avalue such that the polymer Ia or Ib has an intrinsic viscosity of about4 to about 24 dl/g as measured in methane sulfonic acid at RT.

The method of this invention comprises the steps of preparing the rigidrod polymer block in polyphosphoric acid (PPA) followed by addition of acopolymerizable monomer and copolymerization of the same. The rigid rodsegment is prepared according to the following general reactions:##STR2## wherein n and Y are as described previously, and X is --NH₂,--SH, --OH or --NHC₆ H₅.

Following polymerization of the rigid rod segment IVa or IVb, acopolymerizable monomer of the general formula ##STR3## wherein X is aspreviously defined, is added to the reaction mixture containing therigid rod segment, and polymerization of the flexible segments as wellas grafting of these segments onto the rigid rod segments is carriedout.

In carrying out the process, the diamino monomer IIa or IIb is initiallydehydrochlorinated. This is accomplished by mixing the monomer IIa orIIb and terephthalic acid with polyphosphoric acid and heating themixture under an inert gas atmosphere at a temperature ranging fromabout 40° to 100° C. for a period of about 6 to 24 hours. A slightexcess of one of the monomers is employed.

Following dehydrochlorination, the reaction mixture is heated at atemperature in the approximate range of 100° to 200° C. for a period ofabout 18 to 36 hours. In a preferred procedure, the reaction temperatureis increased gradually during the reaction period, e.g., 130° C. for 3hours, 150° C. for 3 hours, 170° C. for hours, 185° C. for 3 hours, and195°-200° C. for 16 hours, or 160° C. for 16 hours and 190° C. for 16hours, or the like. At the end of the reaction period, a small aliquotof the polymer is precipitated from solution into water, washed withwater until acid-free and air dried. If the intrinsic viscosity of thepolymer in methanesulfonic acid is not within the desired range of about8 to 31 dl/g, polymerization is continued until an aliquot sample hasthe desired viscosity.

Once the rigid-rod segment has a desired intrinsic viscosity, asdetermined by one or more aliquot samples, the reaction mixture, iscooled to about 30° to 60° C. and the monomer Va or Vb is added thereto.The resulting mixture is heated under an inert gas atmosphere at atemperature ranging from about 40° to about 100° C. for a period ofabout 6 to 24 hours to effect the dehydrochlorination of monomer Va orVb. Following the dehydrochlorination, the reaction mixture is heated ata temperature in the approximate range of 100° to 250° C. for a periodof about 12 to 36 hours. Aliquot samples may be collected, as describedpreviously, to determine the intrinsic viscosity of the resultingpolymer.

Intrinsic viscosity is determined by extrapolation of η rel-l/c and 1n ηrel/c to zero concentration in methanesulfonic acid at RT.

At the end of the reaction period the polymer is precipitated fromsolution by pouring the reaction mixture into a coagulation bath, suchas water or methanol. If a bulk polymer is desired, the reaction mixtureis poured directly into the coagulation bath, with or without stirring.The polymer may also be formed into fibers by extruding the polymer/PPAsolution through a suitable spinnerette into the coagulation bath. Theresulting fiber may be drawn and heat-treated following knownprocedures.

The relative proportions of the rigid-rod segment to the flexiblesegments can range from about 1:5 to 5:1, preferably 1:3 to 3:1.

The extended chain polymer compositions of the present invention aresuitable for spinning into highly ordered and high strength fibers. Suchfibers are suitable substitutes for other inorganic or organic products.

The following examples illustrate the invention.

EXAMPLE I

2,5-Diamino-1,4-benzenedithiol dihydrochloride (3.04 g, 12.4 mmol) andterephthalic acid (2.08 g, 12.5 mmol) were placed in a 50 ml resin flaskequipped with mechanical stirrer and nitrogen inlet/outlet tubes. 76 gof polyphosphoric acid (84% P₂ O₅) was added to the flask. The resultingmixture was stirred and heated to 40° C. for 8 hours and 70° C. for 12hours to effect dehydrochlorination of the diamino monomer. The reactionmixture was then heated to 160° C. for 16 hours followed by heating to190° C. for an additional 16 hours. A small aliquot of the polymer wasprecipitated into water, washed with water until acid free, then airdried. This sample had an intrinsic viscosity of 12.9 dl/g inmethanesulfonic acid at RT.

To 14.8 g of the above polyphosphoric acid solution containing 0.66 g ofcarboxy-terminated rigid rod, was added 3,4-diaminobenzoic acidmonohydrochloride (3.23 g, 1.7 mmol). After the system was purged withnitrogen, 103 g of polyphosphoric acid (84% P₂ O₅) was added. Theresulting mixture was slowly heated to 100° C. and maintained at thattemperature for 10 hours to effect dehydrochlorination. The reactionmixture was then heated to 200° C. for 3 hours, then 230° C. for 16hours. The viscous solution was cooled to 100° C., precipitated intowater, washed with water, then dried at 140° C. under reduced pressure.Yield 2.16 g (82%).

Analysis for 75% C₇ H₄ N₂.H₂ O-25% C₁₄ H₆ N₂ 5₂ : Calculated: C,62.7;H,3.93; N,18.28 Found: C,60.96; H,3.94; N,18.42

The polymer had an intrinsic viscosity of 10.7 dl/g in methanesulfonicacid at RT. Films of the above block copolymer cast from methanesulfonicacid exhibited the following mechanical properties: Tensile, 40,100 psi;Modulus, 350,000 psi.

EXAMPLE II

The procedure given in Example I was carried out to prepare a likecopolymer containing 50% rigid rod/50% flexible. Films of this copolymerhad the following mechanical properties: Tensile, 9,700 psi; Modulus,1,520,000 psi.

EXAMPLE III

To 0.53 g of a carboxy-terminated poly-para-phenylenebenzbisthiazole(intrinsic viscosity, 17.75 dl/g) was added 88 g of polyphosphoric acid(84% P₂ O₅). The mixture was heated under nitrogen at 160° C. until ahomogeneous solution was obtained. The solution was cooled to 50° C. and1.92 g (0.0093 mol) of 4-amino-3-mercaptobenzoic acid hydrochloride wasadded thereto under reduced pressure. The temperature was maintained at50° C. until dehydrochlorination was complete. The reaction mixture wasslowly heated to 190° C. and maintained at that temperature for 24hours. On cooling to room temperature the polymer was precipitated intowater, washed and dried at 140° C. under reduced pressure.

Analysis for 30% C₁₄ J₆ N₂ S₂ -70% C₇ H₃ NS: Calculated: C,63.13;H,2.80; N,10.51; S,24.09 Found: C,61.31; H,2.48; N,10.26; S,21.90

Intrinsic viscosity 6.5 dl/g.

EXAMPLE IV

Fibers were made by extruding a solution containing 5.8 wt% of the blockcopolymer of Example I in methanesulfonic acid through a single hole 254micron spinnerette into a quenching bath of deionized water at roomtemperature. The coagulated fiber was drawn between two rollers at adraw ratio of 3.4. The fibers were neutralized in ammonium hydroxidesolution over night, washed with deionized water and air dried.

The block copolymer fibers were heat treated by passing them through anoven under constant tension in an air atmosphere. Residence time of thefiber was 30 sec. at 800° F.

The data presented in the following table demonstrate the excellentmechanical properties of these fibers. For comparison the mechanicalproperties of a polybenzimide (PBI) fiber are included.

                                      TABLE                                       __________________________________________________________________________    w % Flexible                                                                              w % rigid                                                                           Youngs Modulus                                                                         Tensile                                                                             Elongation                                   Segment     segment                                                                             (psi)    (psi) at break                                     __________________________________________________________________________    As spun                                                                            70     30    4.83 × 10.sup.6                                                                   13.4 × 10.sup.4                                                              6.5                                          Heat 70     30    15.94 × 10.sup.6                                                                 20.34 × 10.sup.4                                                              1.4                                          Treated                                                                            100 (PBI)                                                                             0    2.09 × 10.sup.6                                                                   9.6 × 10.sup.4                                                               28%                                          __________________________________________________________________________

Various modifications may be made to the present invention withoutdeparting from the spirit or the scope of the following claims.

We claim:
 1. A method for preparing a thermally stable aromaticheterocyclic block copolymer of the general formula ##STR4## wherein mis an integer equal to the number of repeating units of the rigid rodsegment and n is an integer equal to the number of repeating units ofthe flexible end segments, which comprises the steps of(a) reacting1,2,4,5-tetraaminobenzene with terephthalic acid in polyphosphoric acid(PPA) under reaction conditions to form carboxy-terminated rigid rodsegments; (b) adding 2,3-diaminobenzoic acid to the reaction mixture ofPPA and rigid rod segments, and polymerizing said 2,3-diaminobenzoicacid to form flexible segments grafted onto said rigid rod segments; and(c) recovering the resulting block copolymer.
 2. The method of claim 1wherein said reaction step (a) is conducted at a temperature in theapproximate range of 100° to 200° C. for a period of about 18 to 36hours until said rigid rod segment has an inherent viscosity inmethanesulfonic acid at room temperature in the approximate range of 8to 31 dl/g and wherein said step (b) is conducted at a temperature inthe approximate range of 100° to 200° C. for a period of about 12 to 36hours.
 3. The method of claim 1 wherein the relative proportion ofrigid:flexible is in the approximate range 1:5 to 5:1.
 4. The method ofclaim 3 wherein the ratio rigid:flexible is in the approximate range of1:3 to 3:1.
 5. The method of claim 1 wherein said recovery step (c)comprises precipitating said polymer in bulk from solution into acoagulating bath.
 6. The method of claim 1 wherein said recovery step(c) comprises precipitating said polymer by extruding the reactionmixture of PPA and polymer through a spinnerette into a coagulatingbath.